This invention concerns a new catalyst whose characteristics of composition and texture have been specially adapted for the removal, under hydrogen pressure, of metals, particularly nickel and vanadium, contained in petroleum charges such as vacuum residues, reduced crude oils or deasphalted oils obtained by deasphalting these residues. A method of preparing such a catalyst and a hydrorefining process using the catalyst are also provided.
In the catalytic hydrorefining of hydrocarbon fractions of high molecular weight, the decomposition of the metal compounds and, consequently, the removal of the metals is impeded by a certain number of catalytic problems which must be solved if it is desired to proceed to demetallization under the best conditions. A first problem results from the fact that the decomposition of metal compounds involves diffusion limitations to such an extent as sometimes to cause steric hindrance when the considered molecules are asphaltenes of high molecular weight and the catalyst pores have a diameter lower than 50 A; a second problem is due to the fact that the metals, or more exactly the metal sulfides resulting from the decomposition of the metal compounds, accumulate during the operation thus progressively decreasing the initial diameter of the pores and occluding them progressively. A third problem is related to the fact that the metal compounds of the resin or asphaltene type tend, under the operating conditions, to form radicals or radical ions which are specifically very strongly adsorbed on the acid sites of the catalysts; when these acid sites are in the carrier and are too remote from the hydrogenating sites consisting of sulfides of group VIB of the periodic classification promoted by sulfides of group VIII, these resins and asphaltenes tend to dehydrogenate by transfer of hydrogen and then to polycondense, thereby producing products insoluble in the hydrocarbon medium and coke which remains fixed on the catalyst whose activity is accordingly progressively decreased.